Last month Turkey, a Nato member, signed a deal with Russia to buy the missiles, thought to be worth some £1.9bn.

Ankara’s decision to buy the S-400s has been seen in some Western capitals as a snub to the alliance, given tensions with Moscow over Ukraine and Syria, while the deal raised concern because the weapons cannot be integrated into the alliance’s defences.

However, Nato Secretary-General Jens Stoltenberg said this week Turkey was not seeking to antagonise the US-led alliance by purchasing the system and is in talks with France and Italy to buy similar weapons.